1. Field of the Invention
The present invention relates to a method of manufacturing a ferroelectric thin film device, and, more particularly, to a method of manufacturing a ferroelectric thin film device having high crystallinity, good surface roughness and high deposition efficiency through on-axis type sputtering, and to a ferroelectric thin film device manufactured using the method.
2. Description of the Related Art
A ferroelectric material is a material in which spontaneous polarization, caused by a permanent dipole, exists even when an electric field is not applied, and can be inverted by an external electric field. For this reason, ferroelectric materials are used for various electronic devices, such as piezoelectric devices, optical modulators, storage media, memory devices, and the like.
As ferroelectric materials, PbTiO3, BaTiO3(BTO), PbZrxTi1-xO3(PZT), SrBi2Ta2O9(SBT), and the like are well known. Such ferroelectric materials are well known to be suitable for nonvolatile memory devices. FRAM, which is such a nonvolatile memory device and includes an upper electrode, a ferroelectric thin film deposited on the upper electrode and a lower electrode formed on the ferroelectric thin film, records information by applying an electric field to each of the electrodes. The information recorded in the FRAM in this way does not disappear even when the electric field between the upper and lower electrodes disappears because the FRAM has ferroelectric properties.
Particularly, in ferroelectric materials, remnant polarization characteristics are very important. Recently, BiFeO3 (BFO), having higher remnant polarization than other ferroelectric materials, has been researched [J. Wang, J. B. Neaton, H. Zheng, V. Nagarajan, S. B. Ogale, B. Liu, D. Viehland, V. Vaithyanathan, D. G. Schlom, U. V. Waghmare, N. A. Spldin, K. M. Rabe, M. Wuttig, and R. Ramesh, Science 299, 1719(200)].
Such a BFO thin film is required to epitaxially grow in order to maximize the remnant polarization characteristics. Conventionally, the epitaxial growth of the BFO thin film has been conducted through a pulsed laser deposition (PLD) method. However, the PLD method is problematic in that it is difficult to use to form a thin film having a large area, and thus the mass production of the BFO thin film is difficult.
Therefore, as a deposition method suitable for producing the BFO thin film in large quantities, a sputtering method may be used. However, the sputtering method is problematic in that the crystallinity and surface roughness of the BFO thin film are not good due to a problem of resputtering. In a ferroelectric thin film, crystallinity and surface roughness act as very important factors. The reason for this is that the poorer crystallinity and surface roughness are, the more leakage current exists, thus deteriorating data maintenance characteristics.
Further, in order to overcome the resputtering problem, the BFO thin film may be formed through off-axis type sputtering, but such off-axis type sputtering is problematic in that the deposition efficiency is very low, thus decreasing industrial applicability.